This invention relates to parallel arm saws in general and, more particularly, to blade tensioning devices for use with parallel arm saws.
Parallel arm saws for woodworking and other crafts are well known. In the saws, parallel arms are reciprocably mounted to a framework. A saw blade is held between the arms at one end and a mechanism for tensioning the saw blade moves with an up and down motion and a work piece resting on the working surface may be cut by engaging the blade.
One type of blade tensioning mechanism known in the prior art comprises a wedge resting in a groove on th upper surface of the upper arm, a wedge resting in a groove on the lower surface of the lower arm, a bolt passing through both arms and both wedges, a nut threaded on one end of the bolt and a knob threaded ont he other end. When the saw blade is in place, the nut and knob are tightened against the wedges and force the arms toward each other. This forces the arms apart at the other end, causing the saw blade to be held firmly between the arms by tension. Replacing the blade when this type of tensioning mechanism is used can be time consuming as the tension in the blade must be released by loosening the knob. After the old blade is removed and a new blade is inserted, the knob must be tightened down against the wedge in order to create a tension force in the blade. As the knob is being turned, the tension in the new blade must be repeatedly checked to make sure an excessive tension force does not damage the blade. Undue looseness of the blade can likewise lead to damage to the blade and other components. Vibration can also loosen the knob and thus relax the blade tension gradually during operation of the saw.